1. Field of the Invention
The present invention pertains to a method and apparatus for supporting equipment used during intervention operations conducted from marine vessels and/or offshore installations. More particularly still, the present invention pertains to a method and apparatus for compensating for motion encountered during intervention operations conducted from marine vessels and/or offshore installations including, without limitation, operations utilizing coiled tubing, slickline, electric line, wireline, snubbing and/or hydraulic workover units.
2. Brief Description of the Prior Art
As the world's supply of readily accessible oil and gas reserves becomes depleted, significant oil and gas exploration and production operations have shifted to more challenging environments, including deep-water locations. Wells drilled on such locations are often situated in thousands of feet of water, which makes setting of conventional production platforms—that is, support structures permanently anchored to the sea floor—extremely difficult. In certain water depths, installation of conventional production platforms is not possible.
In such cases, wells are typically drilled from floating vessels such as semi-submersible drilling rigs, drill ships and the like. Further, such wells are generally completed using “subsea” completion equipment. In such cases, wellheads and related equipment are situated on the sea floor, while an extensive array of flow lines are used to connect such subsea wells to floating production facilities, pipeline interconnection points and/or other subsea completions.
It is often beneficial to concentrically convey wireline (including, without limitation, slickline, braided line or electric line) and associated tools within wellbores and/or pipelines in order to perform operations in such wells and pipelines. In some cases, hoses or flexible tubing can also be concentrically inserted within a well or pipeline, especially when it is desired to provide a flow path for circulating fluid within said well or pipeline, such as when washing out debris, or when operating fluid-actuated tools in the well or pipeline.
Although the different applications are too numerous to list, in most cases a length of wire or flexible continuous tubing extends from a storage reel or spool and passes through a sheave or gooseneck assembly. Such sheave or gooseneck assembly serves to redirect the wire or flexible continuous tubing into an opening of a wellbore or pipeline, while also reducing the frictional forces acting on said wireline or continuous tubing as it enters the well or pipeline.
Such operations generally do not require specialized equipment when they are performed from fixed platforms or other anchored structures. However, in the case of subsea wells and pipelines, the necessary equipment for performing such intervention operations must typically be mounted on a boat, semi submersible drilling rig or other floating vessel positioned on the surface of the water. In such cases, the boat, semi-submersible drilling rig or other floating vessel can move (pitch and/or roll) with the wave action of the sea, thereby creating slack in the wireline or continuous tubing string and making it difficult to perform such intervention operations on a (stationary) well or pipeline.
As a result, when such intervention operations are performed from boats, drill ships, semi-submersible drilling rigs and/or other floating vessels, it is generally beneficial to maintain substantially uniform tension on the wireline, flexible continuous tubing or other intervention equipment inserted into a well or pipeline. In order to maintain such substantially uniform tension, the distance between the well or pipeline and the intervention equipment should beneficially remain substantially constant.
Thus, there is a need for a dynamic motion compensator that can maintain a substantially constant distance between a well or pipeline, on the one hand, and intervention equipment, on the other hand. Such dynamic motion compensator should beneficially hold substantially consistent tension on wireline, continuous tubing or other intervention equipment conveyed from a floating vessel into a well or pipeline. The motion compensator should beneficially maintain a substantially constant distance between such pipeline or wellhead, and the intervention equipment situated on a boat, semi-submersible drilling rig or other floating vessel.